Scientists looked at the medical records of women whose initial core-needle breast biopsies found rare, yet benign breast conditions: atypical lobular hyperplasia (ALH) or lobular carcinoma-in-situ (LCIS). Follow-up surgical biopsies in which more breast tissue was removed found that up to 25% of the women actually had cancer in addition to their high-risk breast conditions.

Most of the cancers were invasive, meaning the tumours had penetrated normal breast tissue and would require treatment. None of the tumours had spread beyond the breast. "This is very significant," explains lead author Julie A. Margenthaler, M.D., assistant professor of surgery and breast surgeon at Washington University. "We now know that we can't assume that women with ALH or LCIS are cancer free."

In the study, core-needle biopsies found LCIS in 16 patients, and follow-up surgical biopsies detected cancer in four of these women. Of the 19 patients initially diagnosed with ALH, surgical biopsies found that three of them had cancer. The researchers noted no difference between those with cancer and those without in terms of age, number of children, hormonal status or previous breast biopsies - all risk factors for breast cancer.

The cancers detected in the current study are tiny, too small to be felt by a woman or her doctor, says senior author Jill R. Dietz, M.D., assistant professor of surgery and breast surgeon. "In patients who were ultimately found to have cancer, it is likely that the core-needle biopsy simply missed the cancer cells and instead extracted the benign cells."

As a comparison, the study also included 61 women whose core-needle biopsies detected ADH. The more extensive surgical biopsies found cancer in 31 percent of the women who were initially diagnosed with ADH from the needle biopsy.